The present invention relates to an improvement in a pallet assembly for transferring one or more workpieces between locations during which transfer a manufacturing operation takes place. One aspect of the invention is a pallet assembly having parts which are adjustably secured in place whereby the same can be altered as needed to receive workpieces of different sizes. An aspect of the invention is a pallet assembly for transferring a plurality thermoplastic resin preforms through a blow molding operation and thereafter releasing the blown product in connection with which the present invention will be described.
Blow molding thermoplastic organic resins to form hollow containers such as bottles for beer, carbonated beverages, and the like is a known art and is the preferred use for the present invention. Suitable thermoplastic resins include resins which are biaxially orientable such as polethylene terephthalate and polypropylene. The biaxial orientation property requires delivering the resin to the blow mold at a temperature where it can so orient, which is generally within the range between the resin softening point and the resin melting point.
The present invention is called a pallet assembly and provides a means to transport an injection molded preform made of the resin from a preheating oven or other means for adjusting temperature (e.g. through a cooler from the injection mold) to the blow mold thence to a discharge point-- or more broadly from one location where the means is loaded with a workpiece, through a manufacturing location such as a blow molding procedure, then to a second location for discharge.
The present invention is adapted to handle such resin for blow molding in the form of an injection molded hollow preform which in turn is shaped like a test tube that has external threads about its open end. The body of the preform has been heated to an orienting temperature but the threaded end has been kept cool, unheated because such end is not to be blown. Typically, such a preform has a tamperproof ring at the bottom of the threads and a stacking ring underneath the tamperproof ring: the axial space between these rings is preferably the portion of the preform gripped by the pallet of the present invention.
The present invention is deemed an improvement in reheat blow molding of injection molded thermoplastic preforms and provides positive control of the prefrom upon presenting it to the blow mold.
The present invention does not in any way include the peripheral equipment such as the oven; means to transport from the oven to the pallet; pallet loading or unloading means; or the mold design. The present invention relates to a pallet per se which comprises-- a pallet shuttle constituting a base on which the other members of the assembly are mounted; locator means on said shuttle for positively locating said shuttle relative to adjacent machine elements; a workpiece securing and locating assembly supported on said shuttle further comprising guide means mounted on said shuttle, a pair of jaws for engaging a workpiece therebetween mounted on said guide means at least one of which jaws is reciprocably and adjustably to move between closed and open positions which respectively are the positions for securing a workpiece and for receiving or releasing a workpiece, means for biasing said jaws together, a workpiece locating member supported on said shuttle to receive and register a workpiece with reference to said shuttle, said jaws being arranged to reciprocate and hold a workpiece against said locating member, and means supported on said shuttle to move the jaws apart to receive, secure, and release a workpiece.
In the preferred embodiment the pallet is constructed so that it can be adjusted to accommodate different sizes of preforms (workpieces), including means to adjustably mount the jaws so their spacing can be changed and removably mounting the locating member. An annular shaped ring preferably serves as the locating member and vertically locates and centers the preform.